1. Field of the Invention
The present invention relates to a process used for the treatment of the interior surfaces of water supply installations by the removal of solid deposits. More particularly, the present invention is a treating solution and a process for its use, the latter comprising applying an aqueous solution of a mineral acid and hydrogen peroxide to the interior surface of water supply installations, so as to remove calcium-, iron-, and manganese-containing incrustations.
Installations that supply utility or potable water require periodic cleaning of deposits that continuously build up on their interior surfaces. (The term "interior surfaces" includes every portion of the installations that is in contact with water.) These deposits comprise substances dissolved in water that originates from natural sources, and usually consist of iron-, calcium-, and manganese-containing depositions in their carbonate or oxide form. Furthermore, these deposits may comprise ocherous and sinter deposits formed by microorganisms present in soil, especially microorganisms known as iron and manganese bacteria. Incrustations of the ocherous and sinter type possess upon aging considerable resistance to mechanical and chemical attack, and exhibit further resistive power with increasing manganese content.
Installations for the supply of water within the meaning of the present application are, in particular, communal or private installations for the transportation, treatment, and storage of potable and utility water. These installations include tanks, reservoirs, wells, piping, filters, meters, processing plants, aqueducts, towers, tunnels, conduits, etc. In such installations the water is usually at environmental or ground water temperature.
Even though these installations historically consisted of metal or metal parts, presently, synthetic materials are utilized. For example, water storage tanks usually are typically concrete basins coated with a chlorinated rubber.
2. Description of the Prior Art
In the prior art, unsuccessful attempts were made to clean the interior surfaces of water supply installations with the elemental chlorine used to disinfect drinking water. Likewise, mineral acids alone were found not to satisfactorily clean the interior surfaces.
When organic acids such as lactic acid or formic acid were tried, the results were better than with chlorine and organic acids, but still inadequate. Finally, solutions of citric acid, heated to approximately 60.degree. C., were discovered to render relatively satisfactory cleaning. German Pat. No. 20 40 546.
However, the method of the German '546 patent suffered from serious drawbacks. First, preheating the treatment solution to 60.degree. C. uses valuable energy inefficiently as substantial heat is lost to the environment. This problem is exacerbated when cleaning, for example, wells, pipes, or other sunken water supply installations, and reservoirs. Second, according to the German '546 patent, only ascorbic acid leads to acceptable results at normal temperatures, and even large amounts of ascorbic acid are not able to remove particularly stubborn incrustations such as nodular sintered deposits. Third, the use of ascorbic acid, indeed any organic acid, creates a substantial increase in biochemical oxygen demand (BOD) such that the discharge of such cleaning solutions into outfall ditches is prohibited even after neutralization. Finally, in the course of the oxidizing decomposition of organic acids to carbon dioxide, the iron, calcium, and manganese cations bound in them are released, and thereby available for the formation of new deposits.
German Pat. No. 25 20 988 discloses a process for the removal of boiler scale and/or sludge. It should be noted that the composition of these deposits, i.e., little iron and no manganese, differs substantially from the ocherous and sinter deposits removed by the process of the present invention. In the process of the German '988 patent, a two-step treatment is performed wherein the boiler is flushed or treated with an acid solution, followed by treatment with a pure hydrogen peroxide solution. The acid treatment loosens the scale or sludge so that it becomes porous. The hydrogen peroxide treatment bursts the scale or sludge as the hydrogen peroxide penetrates into the pores and dissociates catalytically on the sharp-edged surfaces and/or by the presence of heavy metals. In view of the elemental composition of scale and sludge, no redox reactions occur between the hydrogen peroxide and the substances to be removed. The process of the German '988 patent suffers from the disadvantage that it is a two-step process. More importantly, the process is only slightly effective in removing the manganese-containing incrustations which are readily removed by the process of the present invention.
It is therefore an object of the present invention to provide a process for the efficient removal of solid deposits, particularly manganese-containing incrustations, from the interior surfaces of water supply installations, that may be carried out with a single solution at environmental temperature, and which uses inexpensive, generally available solution components. Furthermore, it is an object of the present invention to provide the aforedescribed efficient removal without a concomitant increase in the biochemical oxygen demand in the outfall facilities.